SPCIFIC AIM 1: Increasing dietary fat intake will raise leptin levels and restore normal gonadotropin and menstrual function in women with hypothalamic amenorrhea (HA). The investigators will investigate the effects of an isocaloric, 300 kcal/day (33 gram) increase in dietary fat to 30% of overall caloric intake over 3 months on: A. Gonadatropin pulsitility and menstrual function, independent of weight or body fat, in women with HA. B. Leptin levels and the diurnal variation of leptin, independent of weight or body fat, in women with HA. SPECIFIC AIM 2: Decreasing dietary fat intake will decrease leptin levels and interfere with normal gonadotropin and menstrual function in healthy eumenorrheic women. The investigators will investigate the effects of an isocaloric, 300 kcal/day (33 gram) reduction in dietary fat to 15% of overall caloric intake over 3 months on: A. Gonadatropin pulsitility and menstrual function, independent of weight or body fat, in healthy eumenorrheic women. B. Leptin levels and the diurnal variation of leptin, independent of weight or body fat, in healthy eumenorrheic women.